digital audio hacks

[Matt Bilsky], an avid reader of Hackaday for years, finally gathered up the courage to submit a project to us. We swear, we don’t byte! Anyway — we’re glad he did, because his project is absolutely awesome. He calls it SnoTunes and it’s a backpack stereo system designed for the outdoors.

It’s a whopping 160 watt stereo, has 7-8 hours of battery life, is somewhat water resistant, and can be controlled wirelessly. Its brain is a Raspberry Pi B+ running Kodi (which was formerly XBMC). A 7″ display is hidden inside of the backpack for more fine tuning controls.

It fetches and downloads YouTube music videos and can create a playlist that can be manipulated by text message. You can share YouTube links to have it download and queue the songs, you can skip the songs (but only if four people make the request), and it even automatically parses the music video titles to extract the song name and band. It also works with AirPlay — but who even uses that.

The biggest and best audiophile projects are usually huge tube amps, monstrous speaker cab builds, or something else equally impressive. It doesn’t always have to be that way, though, as [lowderd] demonstrates with a tiny DIY USB DAC build that turns a USB port into a headphone output.

In the Bad Old Days™ putting a DAC on a USB bus would require some rather fancy hardware and a good amount of skill. These days, you can just buy a single chip USB stereo DAC that still has very good specs. [lowderd] used the TI PCM2707 USB DAC, a chip that identifies as a USB Audio Class 1.0 device, so no drivers are needed for it to work in either Windows or OS X.

The circuit fits on a tiny PCB with a USB port on one side, a headphone jack on the other, and the chip and all related components in between. There are some pins on the chip that allow for volume, play/pause. and skip, but these pins were left unconnected for sake of simplicity.

The board was fabbed up at OSH Park, and the second revision of the case laser cut out of bamboo and acrylic by Ponoko. It’s a great looking little box, and something that fits right inside [lowderd]’s headphone case.

[5 Volt Junkie] has built his share of Arduino projects, but never anything with Python, and certainly never anything with a GUI. After listening to Internet radio one day, a new idea for a project was born: a Raspberry Pi with a small touchscreen display for a UI and displaying soma.fm tracks. It’s finally finished, and it’s a great introduction to Python, Pygame, and driving tiny little displays with the Pi.

Playing soma.fm streams was handled by mpd and mpc, while the task of driving a 2.8″ TFT LCD was handled by the fbtft Linux framebuffer driver. This left [5 Volt Junkie] with the task of creating a GUI, some buttons, and working out how to play a few streams. This meant drawing some buttons in Inkscape, but these were admittedly terrible, so [5 Volt Junkie] gave up and turned on the TV. Tron Legacy was playing, giving him the inspiration to complete his Tron-themed music player.

The result of [5 Volt Junkie]’s work is a few hundred lines of Python with Pygame and a few multicolor skins all wrapped up in a Tron theme. It looks great, it works great, and it’s a great introduction to Python and Pygame.

[Andy] had the idea of turning a mixing desk into a MIDI controller. At first glance, this idea seems extremely practical – mixers are a great way to get a lot of dials and faders in a cheap, compact, and robust enclosure. Exactly how you turn a mixer into a MIDI device is what’s important. This build might not be the most efficient, but it does have the best name ever: digital to analog to digital to analog to digital conversion.

The process starts by generating a sine wave on an Arduino with some direct digital synthesis. A 480 Hz square wave is generated on an ATTiny85. Both of these signals are then fed into a 74LS08 AND gate. According to the schematic [Andy] posted, these signals are going into two different gates, with the other input of the gate pulled high. The output of the gate is then sent through a pair of resistors and combined to the ‘audio out’ signal. [Andy] says this is ‘spine-crawling’ for people who do this professionally. If anyone knows what this part of the circuit actually does, please leave a note in the comments.

The signal from the AND gates is then fed into the mixer and sent out to the analog input of another Arduino. This Arduino converts the audio coming out of the mixer to frequencies using a Fast Hartley Transform. With a binary representation of what’s happening inside the mixer, [Andy] has something that can be converted into MIDI.

[Andy] put up a demo of this circuit working. He’s connected the MIDI out to Abelton and can modify MIDI parameters using an audio mixer. Video of that below if you’re still trying to wrap your head around this one.

[Pat]’s friend got a Pono for Christmas, a digital audio player that prides itself on having the highest fidelity of any music player. It’s a digital audio device designed in hand with [Neil Young], a device that had a six million dollar Kickstarter, and is probably the highest-spec audio device that will be released for the foreseeable future.

The Pono is an interesting device. Where CDs have 16-bit, 44.1 kHz audio, the Pono can play modern lossless formats – up to 24-bit, 192 kHz audio. There will undoubtedly be audiophiles arguing over the merits of higher sampling rates and more bits, but there is one way to make all those arguments moot: building an MP3 player out of an oscilloscope.

Digital audio players are limited by the consumer market; there’s no economical way to put gigasamples per second into a device that will ultimately sell for a few thousand dollars. Oscilloscopes are not built for the consumer market, though, and the ADCs and DACs in a medium-range scope will always be above what a simple audio player can manage.

[Pat] figured the Tektronicx MDO3000 series scope sitting on his bench would be a great way to capture and play music and extremely high bit rates. He recorded a song to memory at a ‘lazy’ 1 Megasample per second through analog channel one. From there, a press of the button made this sample ready for playback (into a cheap, battery-powered speaker, of course).

Of course this entire experiment means nothing. the FLAC format can only handle a sampling rate of up to 655 kilosamples per second. While digital audio formats could theoretically record up to 2.5 Gigasamples per second, the question of ‘why’ would inevitably enter into the minds of audio engineers and anyone with an ounce of sense. Short of recording music from the master tapes or another analog source directly into an oscilloscope, there’s no way to obtain music at this high of a bit rate. It’s just a dumb demonstration, but it is the most expensive MP3 player you can buy.

How do you get 16-bit audio out of an 8-bit microcontroller. We’ll give you a hint: two pins are used. Not helping? Here it comes: two 8-bit DACs PWM outputs are used on this chip, the ATmega1284. One is used for the lower eight bits, the other handles the upper. The two are combined using carefully calculated precision resistor values and the results are beyond what you imagine. This is produced at a bitrate of 44077.135, slightly off from the 44100Hz standard but we challenge you audiophiles to tell the difference. The wave files are served from an SD card read by the chip using the Petit-FatFs library.

There are so many great things about this project. First off, following [Wancheng Zhou’s] example will let anyone with even basic microcontroller skills build a digital audio player for an [Andrew Jackson] and a couple of [Washingtons]. Secondly, those with a medium uC skill level will want to take the idea and implement/debug it for themselves. Bringing it home, [Wancheng] shows how to gauge the quality of the audio output using FFT.

If you didn’t figure it out by the time of year, this is yet another example of a Cornell ECE 4760 final project. Shout out to [Bruce Land] for inspiring awesome projects and requiring extensive documentation of the projects which itself promotes deeper understand all around.

Ever wanted a soundtrack to your life? For a couple of minutes at a time, Signal Snowboards creates that experience with a smart snowboard that varies your music depending on the tricks you perform on your way down the mountain.

The sign on the door says “School For Gifted Hackers”. Inside [Matt Davis] helped interface audio with an accelerometer – something he regularly does with all manner of hacked devices. At first the prototype was an iPhone mimicking the motions of a snowboarder the way fighter pilots describe dogfights with their hands. The audio engine that pulls those mostions to sound is open source and anyone is welcome to do their own tuning.

Once the audio was figured out the boys took it back to their shop and embedded the sensors into a new snowboard. The board is equipped with GPS, an accelerometer, a few rows of LEDs and a bluetooth board to connect to the phone app. It’s all powered by an on-board LiPo battery and a barrel jack out the side to charge it. Channels were cut by hand with a router then electronics sealed in place with epoxy. Not wanting to “just strap some Christmas lights onto a snowboard” the lighting is also connected to the sensors and is programmable.

See the video below of them making the board and taking it out for a test run on Bear Mountain.